1. Field of the Invention
The invention is in the field of radio frequency identification (RFID) devices, and methods for making such devices.
2. Description of the Related Art
Radio frequency identification (RFID) tags and labels have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. RFID tags and labels are widely used to associate an object with an identification code. For example, RFID tags are used in conjunction with security locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,692.
RFID tags and labels include active tags, which include a power source, and passive tags and labels, which do not. In the case of passive tags, in order to retrieve the information from the chip, a base station or reader sends an excitation signal to the RFID tag or label. The excitation signal energizes the tag or label, and the RFID circuitry transmits the stored information back to the reader. The reader receives and decodes the information from the RFID tag. In general, RFID tags can retain and transmit enough information to uniquely identify individuals, packages, inventory and the like. RFID tags and labels also can be characterized as to those to which information is written only once (although the information may be read repeatedly), and those to which information may be written during use. For example, RFID tags may store environmental data (that may be detected by an associated sensor), logistical histories, state data, etc.
In many applications, it is desirable to reduce the size of the electronics as small as possible. In order to interconnect very small chips with antennas in RFID inlets, it is known to use a structure variously called “straps,” “interposers,” and “carriers,” to facilitate inlay manufacture. Interposers include conductive leads or pads that are electrically coupled to the contact pads of the chips for coupling to the antennas. These pads provide a larger effective electrical contact area than those of integrated circuits (ICs). The larger area reduces the accuracy required for placement of ICs during manufacture while still providing effective electrical connection. IC placement and mounting are serious limitations for high-speed manufacture. The prior art discloses a variety of RFID strap or interposer structures, typically using a flexible substrate that carries the interposer's contact pads or leads.
Improvements are desirable in many aspects of RFID devices in general, and in interposers for such devices.